A transmission mask can be made for distortion-free transfer of the structure of a transmission mask to a substrate.
A transmission mask with comparatively simple steps can be used in making dimensionally correct submicrometric structures with 1:1 electron or ion shadowgraphy or with ion or electron projection microlithography.
The transmission mask can comprise a mask foil with a surface structure which has a constant thickness over the entire mask surface as well as openings in the mask foil through which the high-energy beam transmission occurs. To increase the stability of the entire mask structure and thus to guarantee an accurate transmission the openings in the mask foil traverse a grid structure.
With sufficiently small crossbar width the cross members are irradiated by the image forming medium so that a continuous structuring occurs on the substrate to be processed which corresponds to the mask pattern. For wider grid cross members a multiple exposure process can be used in which the image of the image forming medium is displaced so that the cross members no longer appear in the image.
In order to compensate for a rigidity loss which is the result of the openings present, a corresponding strengthening or thickness increase of the grid cross members can be made.
A strengthening of the cross members of the grid is particularly necessary in the case of thermal stressing of the mask foil in order to prevent a nonuniform expansion of the mask foil and thus distortion of the transmitted structure. Although the need for a strengthened grid cross member for a square grid has been recognized where it is desirable to be able to clamp a mask foil in a mask frame having a higher thermal expansion coefficient than the foil, processes to make it have not been devised.